Defines functions and datatypes relating to the singleton for Bool,
including a singletons version of all the definitions in Data.Bool.

Because many of these definitions are produced by Template Haskell,
it is not possible to create proper Haddock documentation. Please look
up the corresponding operation in Data.Bool. Also, please excuse
the apparent repeated variable names. This is due to an interaction
between Template Haskell and Haddock.